The invention relates in general to munitions and in particular to breech-loaded cannon.
Breech-loaded weapons that use bag ammunition require a seal at the breech to prevent propellant gases from passing to the rear into the threads or other parts of the breech mechanism. The traditional method of sealing a breech-loaded cannon uses a rubber donut-shaped ring between forward and rear split rings. The forward and rear split rings and the rubber donut-shaped ring are squeezed between a threaded breech block and the sealing cone of the cannon tube. The forward and rear split rings are able to move annularly about the axis of the spindle when the block is opened or closed. The traditional sealing approach was invented by DeBange in 1872. The DeBange obturator includes five independent parts. The obturator assembly must be inspected and cleaned daily or whenever residue or damage results in a high closing torqure.
A problem with the DeBange sealing method is, when the spindle is removed for daily inspection and cleaning of the obturator seal, the five parts of the obturator seal assembly tend to fall apart. Handling the loose parts is akin to a juggling act. The parts do not readily reassemble correctly. The parts may also fall into hard-to-reach areas where they are difficult to retrieve. In military operations, time is often critical. In addition, aligning and reassembling the parts of the obturator seal assembly typically requires two people.
The problem of loose parts was eliminated with the design of a “one-piece” obturator assembly known as the Crossley obturator and described in U.S. Pat. No. 2,444,633. The Crossley invention introduced new problems. The Crossley assembly uses front and rear rings that are riveted to the rubber donut-shaped ring. Each front and rear ring is comprised of three split segments or arcs. Unlike the DeBange split rings, the Crossley rings' three segments or arcs do not perfectly conform to the sealing cone diameters on the cannon tube. Moreover, the arcs are fixed to the rubber donut-shaped ring using rivets for each arc or segment. Consequently, the areas of the donut-shaped ring where the segmented portions of the rings intersect and flex and the areas of the donut-shaped ring that retain the rivets are repeatedly subjected to extreme burn wear. In addition, the rivets wear on and tear at the rubber donut-shaped ring because the breech block tends to twist the obturator pad (which is held by friction to the cannon tube) as the breech block is opened and closed. The cyclic wear of the Crossley obturator assembly is also high due to the unequal heat expansion of vastly different materials that are riveted together. If any component of the Crossley obturator assembly is damaged, the complete assembly is discarded.
There is a long-felt but unsolved need for an obturator assembly with the advantages of the Crossley and Debange obturator seal assembly designs, but without their disadvantages.